Field of the Invention
The invention relates to a device for measuring the height of a sheet pile by using a reflectively operating radiation detector.
In printing machines, adjustable-height pile tables for sheets are used which, with a lifting device, guide the sheet pile to a separating or singling device. The lifting device is controlled with the aid of measuring arrangements for measuring the height of the uppermost, stationary sheet. In order to assist in the separation, the uppermost sheets are loosened by blown or blast air. The requirements for detecting the height of the pile are thereby made more difficult. The separated sheets are conveyed on a feeder table and fed to the printing machine. As a rule, a great number of constructional elements of the feeder table, the lifting device or equipment for refilling the pile are provided around the pile. Consequently, the options for positioning height detectors are restricted.
The published German Patent Document DE 42 27 814 A1 shows a sheet feeder for a sheet printer, wherein the condition of loosening of the upper part of a pile is registered by two opto-electronic separation-condition detectors, a measurement light beam of which impinges on the pile from above. The detector signals are used to determine the number of floating sheets, by which a separation air flow is controlled.
It is accordingly an object of the invention is to provide a device for measuring the height of a sheet pile which, during the continuous separating operation, permits the height measurement signals to be determined with detectors which are disposed above the pile.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for measuring the height of a sheet pile by using a reflectively operating radiation detector, a sheet separating device and a device for conveying separated sheets to a printing machine being assigned to the pile, comprising a system for measuring the propagation time of a radiation pulse originating from a radiation source and reflected at a sheet surface, the amplitude of the pulse being within a predefined range and lower than the amplitude of the reflection of the same radiation pulse at the surface of the sheet located closest to the radiation source, the radiation detector being connected to the measuring system.
In accordance with another feature of the invention, the radiation source is a sound source.
In accordance with a first alternative feature of the invention, the radiation source is a source for emitting X-rays.
In accordance with a second alternative feature of the invention, the radiation source is a source for emitting a particle beam.
According to the invention, radiation sources, in particular sound sources or radiometric radiation sources which are in pulsed operation are used. Part of the energy of a radiation pulse impinging on the top of the pile is reflected at the uppermost sheet or at a sheet which has just been separated and is being conveyed onward, while a further part of the energy passes through the sheet and is propagated in the direction of the sheet located underneath. The reflection and transmission of radiation energy continue with decreasing intensity on the sheet located underneath. The radiation detector picks up the radiation energy reflected by the sheets. The radiation-detector signals are fed to a system for measuring the propagation time. It is possible for the height of the pile to be derived from the propagation time of the radiation pulse reflected at the uppermost fixed sheet.
The system for measuring the propagation time can be constructed so that the stronger echoes from the outgoing top sheets are filtered out, and only the echoes from the sheets located underneath are evaluated. The transmitting power for the angled arrangement of transmitter and receiver for the radiation is selected so that the weaker echo can also be picked up well.
The sensing location for the radiation detector can preferably be selected at the top of the pile, in the vicinity of the leading or front edge thereof. It is of course possible for a number of radiation detectors to be provided over the format width of the pile, in order to be able to detect curvatures or waves in the pile surface.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for measuring the height of a sheet pile by using a reflectively operating radiation detector, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: